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North American Journal of Fisheries Management

Abstract

Fish screens are designed to divert fish away from potentially life-threatening waterdiversions, yet little is known of the immediate effects of the screens on exposed fish. Todetermine the effects of screen exposure, splittail (Pogonichthys macrolepidotus) swimmingperformance and survival were measured during exposure to a fish screen and bypass channel ina variable-velocity water flume at 12°C for not more than 1.5 h. Four treatment velocities (range,0–60 cm/s) were used with 20 fish (standard length (±SD) = 5.9 ± 1.3 cm) per experiment, withthree replicate experiments per treatment. The sublethal effects of screen exposure were alsoassessed by measuring physiological stress responses at .2, 0, 0.5, 2, and 24 h following screenexposure. No losses of equilibrium or mortality were associated with any of the velocitytreatments. During the control treatment (0 cm/s water velocity through the 0.6-m-wide × 13.7-mlongflume), screen contacts were infrequent (mean total = 2 ± 2), and the mean swimmingvelocity was 18.8 ± 3.5 cm/s. At increased velocities, screen contacts increased, mean swimmingvelocities increased (up to 52.3 cm/s), and the fish displayed significant, positive rheotaxis. Thenumber of fish entering the bypass channel and the physiological stress responses (hematocrit,plasma glucose, and lactate concentrations) did not differ significantly among treatments. Sincesplittail exposed to a wedge-wire fish screen at elevated water velocities similar to those found atlarge water diversions did not experience significant sublethal effects or increased mortality, itdoes not appear that the factors contributing to splittail mortality at diversion screening facilitiesare related to screen exposure.